激光诱导击穿光谱法对钢铁偏析样品的分析

经典判断钢铁样品是否存在偏析带方法有金相显微及硫印方法,其缺点在于分析速度慢,且无法提供元素的含量分布信息。文中在最佳实验条件下,采用激光诱导击穿光谱(LIBS),在空间横向分辨率约为100 μm左右对两块钢铁中低合金板坯及均匀样品扫描分析,在建立校准曲线的基础上,将元素强度二维分布转化为含量二维分布。研究表明,编号为86#样品C,Si,Mn,P,S及Cu等元素存在明显的偏析,编号为174#样品C,Si,P,Ti等元素存在明显的偏析,并对偏析带的宽度进行估算,其偏析带的位置及宽度与金相显微分析方法相吻合。对均匀样品扫描分析,C,Si,Mn,P,S等元素均匀分布,不存在偏析带,通过元素强度或含量二维分布图可间接反映样品的均匀性。与传统的金相分析方法相比较,LIBS不仅可快速准确体现样品偏析带位置及宽度,而且还可同时提供元素含量分布(如C,Si,Mn,P,S等元素)等方面的信息。此方法可用于快速对钢铁样品是否存在偏析带及其宽度进行表怔,从而为钢铁冶炼工艺的改进提供理论依据。     

Influence of surface structure of SiC nano-sized powder analyzed by X-ray photoelectron spectroscopy on basic powder characteristics

SiC nano-sized powder with high specific surface area is potentially of considerable interest to form fully dense SiC ceramics at lower sintering conditions (temperature/pressure). Surface structure of six kinds of commercially available SiC nano-sized powders produced by three different venders was analyzed in detail by X-ray photoelectron spectroscopy (XPS). The overall XPS spectra of all nano-sized powders detected O-based bond (O1s peak), C-based bond (C1s peak) and Si-based bond (Si2s and Si2p peak). Surface structure of nano-sized powders included one of three impurity phases: (1) free carbon, (2) silica and (3) silicon oxycarbide. Furthermore, the influences of surface structure by XPS were systematically investigated on basic powder characteristics, such as chemical composition, morphology, particle density and primary particle size. It was revealed that the basic powder characteristics had a close relationship to the surface structure of nano-sized powder each impurity.     

Stoichiometric changes in the surface of (100) cubic SiC caused by ion bombardment and annealing

The (100) surface of cubic silicon carbide has been studied by Auger electron spectroscopy as a function of in-situ annealing in ultra-high vacuum. The line-shape fine structures for both the silicon and carbon Auger transitions which were destroyed by ion bombardment were readily recovered by a brief heat treatment at about 600°C. Further heating above about 1000°C monotonically decreased the Si/C ratio with increasing temperature. Comparison of the changes in the silicon and carbon Auger peak heights with the intensity for the Ar peak from imbedded argon shows that this decrease in Si/C ratio was caused by silicon depletion rather than by carbon accumulation on the surface. A systematic study of the changes in the silicon and carbon Auger peak heights as a function of time and temperature showed that the depletion occured with an activation energy of about 120 kcal/mole (5.2 eV/atom). The carbon Auger line shape indicates that as the silicon was desorbed, the carbon bonding eventually changed from carbidic to graphitic.     

单壁碳纳米管杨氏模量的掺杂效应

用分子动力学方法研究了N,O,Si,P,S等5种杂质对扶手椅型(5，5)和锯齿型(9，0)单壁碳纳米管杨氏模量的影响.结果表明：直径为0.678和0.704 nm的扶手椅型(5，5)和锯齿型(9，0)碳纳米管在无掺杂时其杨氏模量分别为948和804 GPa.在掺杂浓度10％以下，碳纳米管的拉伸杨氏模量均随掺杂浓度增加近似呈线性下降规律，下降率以Si掺杂最大，N掺杂最小.对与C同周期的元素掺杂，随原子序数增加碳纳米管的杨氏模量下降率增大；与C不同周期的元素掺杂，碳纳米管的杨氏模量随掺杂浓度增加下降率更大，但 关键词： 碳纳米管 杂质 杨氏模量 分子动力学方法     

Dopant-dependence of one-step metal-induced dopant activation process in silicon

We investigate dopant-dependence of low temperature dopant activation technique in α-Si featuring one-step metal-induced crystallization (MIC) to decrease resistivity of p⁺ and n⁺ Si films by forming Ni_xSi_y. Ni not only crystallizes p-type α-Si film but also facilitates activation of boron atoms in the α-Si during the crystallization at 500 °C. However, phosphorus atoms are poorly activated because of the suppressed Ni-MIC rate in n-type α-Si. Finally, p⁺/n and n⁺/p junction diodes are demonstrated on single crystalline Si substrates by the low temperature dopant activation technique promising for high performance TFTs as well as transistors with an elevated S/D.     

Energy levels in doped SiGe quantum well studied by admittance spectroscopy

SiGe/Si quantum wells (QWs) with different Boron doping concentrations were grown by molecular beam epitaxy (MBE) on p-type Si(1 0 0) substrate. The activation energies of the heavily holes in ground states of QWs, which correspond to the energy differences between the heavy hole ground states and Si valence band, were measured by admittance spectroscopy. It is found that the activation energy in a heavily doped QW increases with doping concentration, which can be understood by the band alignment changes due to the doping in the QWs. Also, it is found that the activation energy in a QW with a doping concentration of 2 × 10²⁰ cm⁻³ becomes larger after annealing at a temperature of 685 °C, which is attributed to more Boron atoms activation in the QW by annealing.     

Balance the oxidation resistance and mechanical properties of C/Si–C–N composite by a Si–O–C interphase

Carbon fiber reinforced Si–C–N matrix composite with a Si–O–C interphase (C/Si–O–C/Si–C–N) was fabricated via chemical vapor infiltration and polymer impregnation and pyrolysis process. The mechanical properties and oxidation behaviors of C/Si–O–C/Si–C–N were investigated using three-point-bending test and thermogravimetry. The results indicated that the oxidation resistance of C/Si–O–C/Si–C–N was improved as compared to C/Si–C–N with pyrolytic carbon (PyC) interphase (C/PyC/Si–C–N). The higher oxidation resistance of C/Si–O–C/Si–C–N attributed to the high inoxidizability of Si–O–C interlayer and low thermal stress in matrix. The flexural strength of C/Si–O–C/Si–C–N rivaled that of C/PyC/Si–C–N and the modulus was higher than that of C/PyC/Si–C–N. The suitable interphase and the optimized interface bonding can get the high oxidation resistance of the composites with the mechanical properties maintained.     

Ions and atoms in superfluid helium (4He)

We review the previous conclusion [J.Y. Ryu, Y.C. Chung and S.D. Choi, Phys. Rev. B 32, 7769 (1984)] that the trace property Tr(ABC) = Tr(CAB) leads to two different cyclotron transition absorption formulae in the electron-phonon systems in the lowest order approximation. The pictorial expression and the calculated linewidths in Ge and Si show that the socalled EWC scheme is more seeming than the socalled MWC scheme. The difference is expected to disappear if we take into account all the higher order perturbation terms or start with the many body formalism in the complete scheme.     

氮化铝薄膜的硅热扩散掺杂研究

采用热扩散方法,对AlN薄膜进行了Si掺杂。利用电子能量散射谱(EDS)以及高温变温电导对薄膜进行了分析。EDS测试结果表明:在1 250 ℃的温度下,氮化硅(SiN_x)作为Si的扩散源,可以实现对AlN薄膜的Si热扩散掺杂。高温电流-电压(I-V)测试表明:在460 ℃测试温度下,AlN薄膜在热扩散掺杂以后,其电导从1.9×10^-3 S·m^-1增加到2.1×10^-2 S·m^-1。高温变温电导测试表明:氮空位(V³⁺_N)和Si在AlN中的激活能为1.03 eV和0.45 eV。     

The effect of annealing on the room temperature ferromagnetism in co-sputtered In2O3: C thin films

In this paper, we report investigation of room temperature (RT) ferromagnetism in In₂O₃ (InO) thin films doped with carbon prepared by the co-sputtering method. InO thin films both undoped and C doped with varied thicknesses in the range of 45 to 80 nm were synthesized on Si substrates with varied C concentrations. The carbon concentration was varied from 1.6 to 9.3 at%. The undoped InO films showed no trace of ferromagnetism. Carbon doped films (InO:C) exhibited ferromagnetism at RT, which was of the orders of 10⁻⁵ emu and varied strongly with C concentrations. It is observed that the magnetization reached a maximum value of 5.7 emu/cm³ at 4 at% C. Annealing of the InO:C films in an oxygen environment resulted in a decrease in the magnetization, indicating the crucial role of oxygen vacancies in the films. It is concluded that the oxygen vacancies were important and compete with C substitution for the RT ferromagnetism.     

Carbon-coated Si/graphite composites with combined electrochemical properties for high-energy-density lithium-ion batteries

Carbon-coated Si/graphite composites with different Si/graphite weight ratio have been fabricated using solid-state reaction with aim to improve the cyclic stability, coulombic efficiency, and rate capability simultaneously. Microstructural investigation reveals that the Si particles are covered by amorphous carbon and attached to the carbon-coated graphite surface. Electrochemical evaluation has been performed using cyclic voltammetry and charge/discharge cycling at different current densities, which indicate that addition of graphite can not only enhance the first-cycle coulombic efficiency to 90 % but also improve the cyclic stability drastically. The carbon-coated Si/graphite composite with appropriate contents of Si, graphite, and carbon is expected to be promising candidate as anode materials for high-energy-density lithium-ion batteries.     

13C qNMR结合DFSS方法测定油品芳碳率

利用六西格玛设计（design for six Sigma,DFSS）方法,通过定量核磁共振碳谱（quantitative carbon nuclearmagnetic resonance spectroscopy,¹³C qNMR）对由11种已知烃类化合物组成的模型油品进行了芳香碳摩尔百分比C（ar）%,简称芳碳率]测定的系统研究,建立了C（ar）%与样品浓度Conc.、弛豫试剂浓度[Cr（acac）₃]和循环延迟D13个参数之间的数学模型,据此模型得到了优化的参数设置：Conc.为180 mg/mL,[Cr（acac）₃]为12 mg/mL,D1为10.5 s.按此设置进行了8组验证实验,其结果重现性较好,相对标准偏差（relative standard deviation,RSD）为0.61%;准确性较高,达到99.0%~100.6%.该方法也可用于其它分析测试方法的系统研究,且实验结果对现行油品芳碳率测定标准中相关参数,如[Cr（acac）₃]和D1的设置能够提出补充性建议.     

Si/polyaniline-based porous carbon composites with an enhanced electrochemical performance as anode materials for Li-ion batteries

Silicon/polyaniline-based porous carbon (Si/PANI-AC) composites have been prepared by a three-step method: coating polyaniline on Si particles using in situ polymerization, carbonizing, and further activating by steam. The morphology and structure of Si/PANI-AC composites have been characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Raman spectra, respectively. The content and pore structure of the carbon coating layer in Si/PANI-AC have been measured by thermogravimetric analysis and N₂ adsorption-desorption isotherm, respectively. The results indicate some micropores about 1~2 nm in the carbon layer appear during activation and that crystal structure and morphology of Si particles can be retained during preparation. Si/PANI-AC composites exhibit high discharge capacity about 1000 mAh g^?1 at 1.5 A g^?1; moreover, when the current density returns to 0.2 A g^?1, the discharge capacity is still 1692 mAh g^?1 and remains 1453 mAh g^?1 after 70 cycles. The results indicate that the porous carbon coating layer in composites plays an important role in the improvement of the electrochemical performance of pure Si.     

Surface structure of low-coveraged Cs on Si(0 0 1)-() system

Alkali metals (AM) on semiconductors have been investigated as a simple model system for the metal-semiconductor interfaces due to their simple electronic structures. Especially, cesium (Cs) on Si(0 0 1) surface has been studied with various experimental techniques. In this study, we investigated the atomic structure of initial Cs adsorption on Si(0 0 1)-(2×1) surface using coaxial impact collision ion scattering spectroscopy. When Cs atoms are adsorbed on Si(0 0 1)-(2×1) up to 0.2 ML at room temperature, the initial adsorption site is on-top T3 site with poor periodicity and the length of Si dimer is reserved as in the clean Si(0 0 1) surface. It is also found that Cs atoms adsorbed on Si(0 0 1) surface with a height of 2.83±0.05 Å from the second layer of Si(0 0 1) surface.     

Palladium clusters in nanoporous carbon samples: Magnetic properties

The magnetic properties of nanoporous carbon samples were studied. The samples were prepared from silicon and boron carbides and contained palladium clusters incorporated into pores. Electron spin resonance (ESR) studies over a wide temperature range (3–100 K) showed that the palladium clusters have a significant effect on the electrical and magnetic characteristics of composite samples. In particular, the ESR spectrum of samples with palladium has a narrow line whose intensity varies with temperature following the Curie law, which indicates the formation of an ensemble of localized spins. Therefore, the hole conductivity of the carbon skeleton is partially compensated. The ESR spectra of C(SiC): Pd have a ferromagnetic resonance line, which suggests that some Pd clusters in pores are magnetically ordered. This line is absent in C(B₄C)B: Pd samples. However, the small variation of the resonance frequencies with temperature indicates that the C(B₄C): Pd samples also contain small magnetic inclusions. Original Russian Text ? B.D. Shanina, A.M. Danishevskiĭ, A.I. Veynger, D.A. Kurdyukov, S.K. Gordeev, 2009, published in Fizika Tverdogo Tela, 2009, Vol. 51, No. 3, pp. 596–603.     

Early Aptian carbon and sulphur isotope signatures at ODP site 765

Current carbon and sulphur isotope ratios (δ(13)C and δ(34)S) suggest there were major shifts in partitioning between reduced and oxidised reservoirs of carbon and sulphur during the Early Cretaceous. However, the δ(13)C and δ(34)S records are composed from different Ocean Drilling Program sites and are hard to correlate at high resolution. We present high-resolution Aptian δ(13)C(org) and δ(34)S(barite) values derived from the same set of samples, enabling a higher certainty correlation than previously possible. Two major hypotheses aim to explain the Early Aptian S-isotope excursion: increased volcanic degassing and/or fluctuations in the marine sulphate concentration. Our S-isotope data provide tight constraints on the timing and magnitude of volcanic flux required. We show that the observed S-isotope signature can be explained by a 2?Ma pulse of increased volcanic flux, injecting ～4.5×10(18)?mol C into the atmosphere. Further work is needed to evaluate whether these fluxes are compatible with the existing C-isotope record.     

Carbon-coated silicon/crumpled graphene composite as anode material for lithium-ion batteries

Silicon is a promising anode material for high-capacity Li-ion batteries (LIBs). However, its insulating property and large volume change during the lithiation/delithiation process result in poor cycling stability and in pulverization of Si. In this work, glucose-derived carbon-coated Si nanoparticles (C–Si NPs) are in conjunction with crumpled graphene (cGr) particles by a spray-drying method to prepare a novel composite (C–Si/cGr) material. The prepared C–Si NPs are uniformly embedded in the ridges of the cGr particles. The carbon layer of C–Si can make a good contact with the graphene sheet, resulting in enhanced electrical conductivity and fast charge transfer. In addition, the unique crumpled structure of the cGr can buffer the large volume change upon cycling process and facilitate the diffusion of electrolyte into the composite material. When employed as an anode electrode of LIBs, the C–Si/cGr composites deliver enhanced electrochemical performance, including stable cycling with a discharge capacity of 790 mAh·g⁻¹ after 100 cycles and a rate capability of 654 mAh·g⁻¹ at 2C. The synergistic effect of the carbon layer coating of Si NPs and the crumpled structure of the cGr particles results in a composite with improved the electrochemical performance, which is likely related to its high electrical conductivity and good mechanical stability of composite material.     

P–n junction characteristics of graphene oxide and reduced graphene oxide on n-type Si(111)

The semiconductor behavior of graphene oxide (GO) and reduced graphene oxide (RGO) synthesized by the Hummers method on n-type Si(111) were investigated. Graphene oxide is a product of the oxidation of graphite, during which numerous oxygen functional groups bond to the carbon plane during oxidation. RGO was prepared by adding excess hydrazine to the GO showing p-type semiconductor material behavior. In the C–O bond, the O atom tends to pull electrons from the C atom, leaving a hole in the carbon network. This results in p-type semiconductor behavior of GO, with the carrier concentration dependent upon the degree of oxidation. The RGO was obtained by removing most of the oxygen-containing functionalities from the GO using hydrazine. However, oxygen remaining on the carbon plane caused the RGO to exhibit p-type behavior. The I–V characteristics of GO and RGO deposited on n-type Si(111) forming p–n junctions exhibited different turn-on voltages and slope values.     

Initial growth process and surface structure of Ag on Si(111) studied by low-energy Ion-Scattering Spectroscopy (ISS) and LEED-AES

The growth process of silver on a Si(111) substrate has been studied in detail by low-energy ion-scattering spectroscopy (ISS) combined with LEED-AES. Neon ions of 500 eV were used as probe ions of ISS. The ISS experiments have revealed that the growth at room temperature and at high temperature are quite different from each other even in the submonolayer coverage range. The following growth models have been proposed for the respective temperatures. At room temperature, the deposited Ag forms a two-dimensional (2D) island at around 2/3 monolayer (ML) coverage, where the Ag atoms are packed commensurately with the Si(111)1 substrate. One third of the substrate Si surface remains uncovered there. Then it starts to develop into Ag crystal, and at a few ML coverage a 3D island of bulk Ag crystal grows directly on the substrate. An intermediate layer, which covers uniformly the whole surface before the growth of Ag crystal, does not exist. At high temperatures (>~200°C), the well-known Si(111)√3-Ag layer is formed as an intermediate layer, which consists of 2/3 ML of Ag atoms and covers the whole surface uniformly. These Ag atoms are embedded in the first double layer of the Si substrate. It is concluded that the formation of the √3 structure needs relatively high activation energy which may originate from the large displacement of Si atoms owing to the embedment of the Ag atoms, and does not proceed below about 200°C. The most stable state of the Ag atoms on the outermost Si layer is in the shape of an island, both for the Si(111) surface and for the Si(111)√3-Ag surface.